A senior republican whose arrest over an IRA-linked murder escalated the current political crisis in Northern Ireland has accused unionists of using his "wrongful detention" to try to pull down power sharing.

Sinn Fein's northern chairman Bobby Storey speaks during a press conference at the Roddy McCorley Social Club in west Belfast

Bobby Storey was arrested by police investigating a murder by Provisional IRA members

Sinn Fein president Gerry Adams speaks during a press conference at the Roddy McCorley Social Club in west Belfast

A senior republican whose arrest over an IRA-linked murder escalated the current political crisis in Northern Ireland has accused unionists of using his "wrongful detention" to try to pull down power sharing.

Sinn Fein northern chairman Bobby Storey and two other well-known republicans were taken into custody on Wednesday. They were released without charge on Thursday night.

But during the period they were being questioned by detectives, Stormont's First Minister Peter Robinson stepped down and three of his Democratic Unionist ministers quit the Stormont coalition Executive.

The DUP mass resignation threat and subsequent walkout was prompted by the three arrests, amid claims the investigation into the shooting of former IRA man Kevin McGuigan had reached into the senior levels of Sinn Fein.

The Ulster Unionists pulled out of the Executive last month, claiming trust in Sinn Fein has been destroyed.

Commenting publicly on his arrest for the first time, Mr Storey said: "I absolutely reject the attempts of the unionist parties to cynically use these murders and my wrongful detention to threaten these political institutions."

Police have said current members of the IRA were involved in last month's shooting of Mr McGuigan in a suspected revenge attack for the murder of former IRA commander Gerard "Jock" Davison in Belfast three months earlier.

The disclosures about the IRA have heaped pressure on Sinn Fein to explain why the supposedly defunct paramilitary organisation is still in existence.

Sinn Fein has insisted the IRA has gone away and has accused the two unionist parties of contriving a crisis for electoral gain.

Mr Storey added: "The behaviour of the unionist parties, who have cynically used my arrest to pull down the political institutions, has been nothing short of disgraceful.

"They have succeeded only in holding the political process to ransom and providing encouragement to the dissident elements and the criminals who murdered Jock Davison and Kevin McGuigan."

Mr Storey said he had "serious concerns" over his arrest, and the timing of it and claimed "not a shred of evidence or intelligence" was presented to him during questioning.

But he backed the PSNI as the appropriate body to investigate the two murders.

The republican veteran said the "IRA has gone away" and was "not coming back".

"The people who murdered both men are criminals and enemies of the Sinn Fein peace strategy," he said.

"Every effort must be made to ensure they are brought before the courts to face due process."

Intensive political talks aimed at saving power sharing will convene in Belfast tomorrow.

There have been questions over whether unionists will attend the set piece negotiations.

The Ulster Unionists confirmed they would be there "all things being equal".

The UUP criticised a negotiation initiative last week for not scheduling the murder as the first item on the agenda.

The coalition government is teetering on the brink of collapse after the DUP last week pulled all but one of its ministers out of the administration.

Fresh talks involving the main parties and the British and Irish governments will be convened by Secretary of State Theresa Villiers at Stormont House.

They will focus on the fallout from the murder and a range of other destabilising disputes threatening the future of the Stormont Executive, including the bitter impasse over implementing welfare reforms.

During the event in west Belfast, Mr Storey repeatedly insisted the IRA was no more - at one stage evoking the metaphor of a butterfly.

"The IRA has gone, the IRA have stood down, they have put their arms beyond use, they have left the stage, they are away and they are not coming back," he said.

"There is no current status of the IRA, there is no current IRA members - the IRA has gone."

Police Service of Northern Ireland (PSNI) chief constable George Hamilton has said there is no evidence IRA leadership sanctioned the McGuigan murder. However, the region's senior officer said structures of the organisation still exist, albeit for political, not terror, purposes.

Mr Storey said he agreed with the assessment there was no IRA military footing, but he added: "Where I differ from the chief constable, is there is no role for the IRA, the IRA has finished, the IRA has gone. I think the chief constable and other perspectives out there see this in terms of the IRA being the caterpillar that's still there, where I think it's moved on, it's become a butterfly, it's flew away, it's gone, it's disappeared and they need to evolve to that as well.

"They need to move on to a different level of where this has got to. Not only is there no IRA, there is no logic for an IRA. The primary republican organisation and the primary republican morality, credibility and representativeness is in the Sinn Fein party."

DUP MP Gregory Campbell said he did not believe Sinn Fein denials about the IRA.

"Bobby Storey is like Gerry Adams and a growing list of republicans whom people in the unionist community simply don't believe," he said.

"Whilst Storey says the PIRA is gone, the Chief Constable, the Secretary of State and a host of others disagree.

"Unfortunately for republicans, nearly everyone else believes the Chief Constable rather than Bobby Storey or Gerry Adams. The problem with this latest drivel is that it compares the IRA to butterflies. Action on what they intend to do about the IRA is what is needed as opposed to this latest idealistic nonsense. The murder of two men in recent weeks significantly contradicts the words of people like Bobby Storey.

"Republicans are threatening devolution."

The East Londonderry representative said the DUP was trying to "create the time and space to allow negotiations".